Azidophenylalanine (4-azido-<small>L</small>-phenylalanine) is an unnatural amino acid derivative of <small>L</small>-phenylalanine, featuring an azide group at the para position of the phenyl ring. It is a bioorthogonal click-chemistry reagent that can be genetically incorporated into proteins via expanded genetic code techniques for site-specific labeling and functionalization. The compound serves as a vibrational reporter for local protein environments due to its azide group and is used in photo-crosslinking for protein interaction studies.
Azidophenylalanine has the molecular formula and a molecular weight of 206.20 g/mol. Its IUPAC name is (2S)-2-amino-3-(4-azidophenyl)propanoic acid. It appears as an off-white solid and is soluble in water, DMSO, and DMF.
As with many other azides, the isolated compound exhibits explosive properties. It is light-sensitive and should be stored at -20 ðC in the dark.
A chromatography-free synthesis of azidophenylalanine has been reported. It starts from <small>L</small>-phenylalanine and includes iodination to form 4-iodo-<small>L</small>-phenylalanine, followed by Boc protection, Cu(I)-catalyzed azidation using sodium azide (NaN<sub>3</sub>), deprotection with sulfuric acid, and purification by recrystallization. This method avoids explosion risks associated with earlier approaches.
As an analog of <small>L</small>-phenylalanine, azidophenylalanine is incorporated into proteins during translation in place of phenylalanine. The azide group enables bioorthogonal reactions, such as copper-catalyzed or strain-promoted azide-alkyne cycloadditions, for protein modification.
Azidophenylalanine is employed in metabolic labeling to detect nascent protein synthesis as a non-radioactive alternative to traditional methods. It facilitates site-specific protein labeling for microscopic imaging, purification, and FRET studies. Applications include photochemical control of fluorescent proteins, synthesis of ligands for metal complexation in EPR/NMR, and probing protein dynamics during folding or catalysis. It is incorporated using orthogonal tRNA/synthetase pairs in systems like E. coli.